qemumips: Use 34Kf CPU emulation

qemumips: Use 34Kf CPU emulation

Few years ago we switched to using mips32r2 tunings for qemumips however
the default CPU emulation still remained 24Kf which is not optimal for
mips32r2 ISA for qemu [1], therefore switch to recommended 32Kf for CPU
emulation when running qemu in system mode

Boot time to console is ~1s faster with this setting, hopefully this
should speed up qemumips in general

[1] https://www.qemu.org/docs/master/system/target-mips.html#preferred-cpu-models-for-mips-hosts

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>